Then i found new folder called: VST plugins with 2 new acustica folders, this is confusing as i already had these folders for my old version and expected that old one to be upgraded.

So i found the new versions, still called Nebula3CoreII64 Reverb? Another confusing bit. SO i load this new .dll and get the following message:
Acustica loader ver 1.3.600
1 DEBUG level: 0
2 Master Ko:Master decriptor not found (Nebula3CoreII6
4 reverb.xml)

Questions i have:
1: do i need to just delete the files and try again with other destinations?
2: will all my Nebula custom setups be updated?
3: will old librarys be accesible in the future? especially since some library developers quit existing.
4: how do i properly install 1.3.600 or what i have to do to make it work?

If you have an "old" computer (lol, even a 4 year old Core 2 Quad counts as old), you may need to either revert back to 1.3.505 or wait for the temporary 1.3.601 that Ginacarlo announced a few days ago (it may be in the downloads section, I haven't looked yet). I had a terrible time with 1.3.600, but many Windows users report flawless performance I guess.

Yeh me too. Suspect Ill have to wait for a non-developer to confirm theyre running server on windows before I risk it again

If you need a new version to use a new library (like Gemini's G2500), the bug-fix update is in the download are now. I have been using that with zero problems so far. But I also have a spare copy of the 1.3.505 instal files handy, just in case......

I asked support about it and received a broken English single sentence saying I should ask in the bug forum or downgrade. WTF? Why do I request support, only to be redirected to a forum.

Anyway, the x64 version seems to be install new .DLL and new .xml files to a VSTplugins\Acustica64 folder (where the old 505 version was installed to VSTPlugins\Acustica.

So now Reaper shows 'Nebula3' and 'Nebula3CoreII64' (the later is the old version I assume?). The 'Nebula3' looks completely different to the older version, just like the screenshot the original poster posted (mine is at http://clients.maxx-traxx.eu/Clipboard01.png).

As you see in the shot, this is with the 1.3.601 'bugfix' version. I re-installed the x86 version from scratch (by running the 1.3.492 setup, installing my license again, and upgrading to 1.3.505, 1.3.600, 1.3.601) and it looks just like the old version and seems to be running fine.

Then I installed the x64 version the same way. Started from 1.3.492 x64 setup, installed my license. Works. Upgrade to 1.3.505 x64, works. Upgrade to 1.3.600, fails with the same screen as my screenshot. Upgrade to 1.3.601, still the same as the screenshot.

Thats exactly it Rich. Im in no hurry to get into the upgrade tangle again though.. Ive purchased g2500 already, I expect great things

Why do I request support, only to be redirected to a forum

I experienced this too and I think because acustica was inundated with questions exactly like mine. Mostly posted in the wrong place(mine were.)

What I cant get my head around though is an upgrade, available as an upgrade to an existing server installation - that wont work until you 1st install the neb pro installation program for that version, before you run the upgrade, while this vital bit of information is buried somewhere on a page in another forum talking about how to install... the upgrade .exe should have included the neb pro installation files.